This invention pertains to arrangements for performing electrical tests on contact material samples, and in particular for testing contact material test samples in an evacuated environment under high current loads. Frequently, it is desirable in developing high-current separable contact material, to have at least a preliminary analysis of selected candidate conductor materials. Testing of material samples will hopefully identify materials unsuitable for high current electrical contact without requiring incorporation of the materials into a completed and oftentimes complex structure.
An example of a project requiring preliminary testing of contact materials is that of determining segmented first wall connectors on fusion devices, particularly Tokamaks. Current Tokamak designs require easily separable connectors between first wall segments, that can handle the large currents required for plasma confinement. Generally, the amount of current that connectors can safely carry depends on physical characteristics of the connector arrangement. Important characteristics include the size of the connectors, the force with which they are pressed together, and their inherent physical properties such as conductivity, melting point, and oxidation resistance. The choice of successful candidate materials also depends on the nature of the applied current, particularly the wave-form shape, pulse ramp-up-time or rise time of the current.
Some material samples, such as the aforementioned Tokamak connectors, operate in a high vacuum environment. An accurate materials test for such samples must therefore be provided in a similar vacuum, since contact performance depends on the presence or absence of various components found in an ambient air environment. For example, oxidation rate and carbon formation will differ greatly between evacuated and ambient environments.
Prior art test arrangements were designed as an electrical test apparatus which did not incorporate a vacuum system. These arrangements were designed to be placed in an evacuated chamber (when such was required), and the electrical power test connections as well as the instrumentation connections had to penetrate the vacuum vessel barrier.
Circuits containing high currents experience correspondingly high magnetic forces. It is imperative that a controlled contact pressure with the material sample be maintained during current tests. This is especially important when high test currents are employed, since the magnetic forces can tend to separate a material sample from its test assembly contacts, thereby causing an erroneous impression of the material samples current handling performance. If an accurate test of the current handling ability of material samples, particularly reduced size samples is to be obtained, any pulsed or alternating test currents must flow symmetrically through the sample.
It is therefore an object of the present invention to provide a test assembly suitable for performing high-current tests on samples efficiently and with a minimum of preparation.
Another object of the present invention is to provide an assembly for testing the maximum current density and pulse that a material sample can absorb without sticking, welding, melting, or jumping apart.
A further object of the present invention therefore is to provide a materials test assembly that can easily accommodate material samples of different sizes and surface properties, while providing a simple and accurate control over the pressure applied to the samples.
Another object of the present invention to provide an evacuated test assembly to simulate a high vacuum environment.
A related object of the present invention is to provide an evacuated test assembly having vacuum-vessel-compatible power feed, vacuum system and instrumentation connections, in which rapid and simple exchange of test samples within the vacuum environment is possible.
An additional object of the present invention is to provide a test arrangement that eliminates the vacuum interface connection of these power circuits.
Yet another object of the present invention to provide a test assembly in which a controlled pressure on material samples is maintained, despite magnetic forces impressed upon system members by reason of the test currents.
A further object of the present invention to provide a test assembly in which test currents are distributed symmetrically throughout the material sample.
Another object of the present invention to provide a compact test assembly arrangement comprised of a minimum number of inexpensive parts and which affords as high a degree of portability as is practicable.